HP recovery is faster when your HP is at a lower percentage than it is at a higher percentage (i.e. you heal fast, but it gradually slows as you heal). This would mean it’s an advantage in terms of turns spent to rest only when injured.

Water elementals’ HP (and Pw, if applicable) regeneration is boosted when they are on a water-containing space such as a moat or a fountain. Possibly, they can also suck up the water to regain a large quantity of hit points at once, which removes the water terrain if it is expendable (a fountain or pool or puddle of shallow water will dry up).

In order to make them more interesting in combat, their AI may favor hanging around sources of water and trying to find a path to the nearest water when they are injured.

Add two new elemental planes, those of Positive Energy and Negative Energy.

The Plane of Positive Energy:

• The full level is lit.
• Has lots of yellow lights, trees, and whatever plant-based monsters exist in the game.
• Everything is treated as if it has regeneration. The player can regenerate current HP past its maximum, but if this gets too far past the maximum, they instantly die from being unable to contain the energy (there are warning messages to this effect as you approach this point).
• Items in the player’s and monsters’ inventories can randomly get blessed, enchanted, or charged - even if this runs the risk of overenchanting and destroying them.
• Eating any food restores HP as well as nutrition.
• All exercisable attributes are exercised at regular intervals.
• All sleep effects are negated.

The Plane of Negative Energy:

• The full level is dark.
• Contains lots of undead.
• Everything constantly loses hit points. If you have regeneration, it either nullifies or only partly nullifies this effect.
• Items in the player’s and monsters’ inventories can randomly get cursed or lose enchantment or charges (going negative on things which are capable of being negative).
• You lose several times as much nutrition per turn as normal.
• All abusable attributes are abused at regular intervals.

The rate at which HP regenerates when resting on a bench isn’t constant. It starts out slow (less than 1 HP per turn), then speeds up gradually the longer you sit on it, eventually capping at 2-4 HP per turn.

Change the HP and/or Pw regeneration formulas (natural regeneration, not from external sources) so that it regenerates faster in the early game but more slowly in the late game.

This fixes existing balance problems – that the hero doesn’t regain them fast enough early on, and by later on they regain them so fast it trivializes problems – but would be very strange to justify flavor wise.

In a lot of folklore, iron wards away elves. This could be implemented in the game in several ways:

• Elves take extra damage when hit by iron. Not as much as silver, but still appreciable.
• Elven players take a small amount of damage when putting on or wielding iron gear, but get no further penalty. (dnethack hurts their regeneration rate while wearing iron, which is another option).
• Possibly some detrimental effect when wielding iron weapons as well, a to-hit or damage penalty, or negating bonuses from dexterity, strength, and skill, or something.
• This is balanced by elven racial equipment being better (not improved; it’s already better).

“The Amulet of Vitality”, an amulet of drain resistance that provides poison resistance and hungerless regeneration when worn and also increases your HP maximum by 20%.

Note: this could be implemented in a game that doesn’t have the amulet of drain resistance by instead making its base item the amulet versus poison and giving it drain resistance when worn.

You are only capable of regenerating health when you are standing still in one place, resting (or searching). Continuing to move around the level or fight things does not allow you to passively heal.

The player’s natural HP regeneration rate is brought down to zero upon taking any damage or non-damaging hit, then gradually increases over time back to its full rate.

Potion of regeneration. Grants some medium duration (maybe fifty to a hundred turns) of temporary intrinsic hungerless regeneration. Can be brewed using healing potions, perhaps, but should be fairly rare in terms of random generation.

A new branch with infinite levels, whose level difficulty continues steadily increasing the deeper you go. Monsters killed do not drop anything, except that there is a very small chance, increasing with greater difficulty, of dropping a single wand of wishing. Unlike the rest of the dungeon, monster generation cares only about the level difficulty, ignoring the player’s experience level.

Levels in this branch are non-persistent. To prevent destroying any unique items, you either can’t bring them into the branch at all, or you are prevented from leaving a level in any way while they are on the level somewhere other than your person. Not determined what drinking a cursed potion of gain level would do.

One way to increase the challenge and prevent the hero from resting on the downstairs every level and starting each new level fresh is to suppress or remove natural HP regeneration in this branch.

Using an upstairs will take you back to the branch entrance, which may then close off forever. Possibly, 9/10 of upstairs will just crumble to nothing upon arrival in the level (whether this 9/10 is random or happens regularly every 10 levels isn’t determined). This makes it less easy to decide to bail out, though levelport or branchport would probably still work as escape items.

Not determined is to what degree the branch should enforce the player to spend time on each level. The three proposed options are:

1. No enforcement. The player can go as deep as they want by digging a hole right away with the increased risk it entails.
2. Enforced finding the downstairs. The floor is nondiggable, so the player has to at least reach the downstairs in order to travel further.
3. Enforced battling a certain amount (or all) of the monsters. The downstairs will not let you travel down them unless you have killed a certain amount of monsters on the level.

Merge the rings of slow digestion and regeneration. Keep the name “regeneration”; make it chargeable. A positive rate boots your regeneration and your hunger rate, up until they are doubled at +10; a negative rate decreases both until they are halved at -10, with the intermediate values scaling as appropriate.

Possibly, since the extremes of &177;10 are hard to attain, make the doubling/halving threshold at &177;7 instead.

Hungerful regeneration from the ring only costs excess nutrition if your HP is actually below full. Possibly, to compensate for not having to micromanage your ring finger, accelerate the hunger rate while regenerating HP: instead of double, perhaps triple or quadruple its usual rate.

The amulet of restful sleep confers hungerless regeneration whenever the player is asleep.

Golems do not regenerate hit points, and healing spells do not work on them.

Regenerating HP naturally doubles your hunger rate while you are regenerating.

Condensing all of NetHack’s poison mechanics into one unified mechanic:

• Dexterity and Constitution poisons are removed. Quasits (the only AD_DRDX attack) might still directly harm Dex, but it’s no longer flavored as poison. Rabid rats (the only AD_DRCO attack) don’t cause poison, they cause disease, which hits Constitution. Poison will now only affect Strength.
• Poison is now implemented as a timing-out trinsic. The amount of Str loss is a direct function of how much timeout is left, so Str will gradually recover as the poison goes away.
• Passing Con saving throws could give small bonuses to decreasing the timeout faster than normal.
• While poisoned, HP regeneration is either impeded or stopped entirely, or else the player’s HP is damaged every turn, or every several turns.
• It could also heavily abuse Str while it lasted instead of being directly tied to Str.

In order to make extrinsic regeneration scale better, it acts as a multiplier to your natural regeneration rate. x2 is an option but may be too high; x1.5 might work better.

Another idea is to make it so that regeneration gets better the closer you are to dying of HP loss, formally: if current HP = X * maxHP, regeneration will heal you at a rate of (2 - x) times its normal rate.

Change the sickness instadeath to a HP-based form of damage, since it is very obscure about how long you have left to live and can be drastically reduced.

• Instead of a death timer, apply a penalty to HP regeneration rate, with this penalty being variable and slowly decreasing as you recover from the sickness. This is nice because it allows for monsters to have a sickness attack in the early game.
• This penalty can be large enough to make your regeneration rate negative.
• Getting hit by a sickness attack while already Ill not only increases the severity/duration of your illness, it deals some extra damage proportional to the severity of the sickness.
• Severe enough sickness only partially times out - you will need to take some actual self-healing action like quaffing healing potions, praying, casting cure sickness, applying a unicorn horn, etc. to be completely cured.
• Unicorn horns no longer cure the entire illness all at once - they will only reduce the severity (which might cure the illness all at once if it’s mild).
• Being sick for a long time may cause vomiting, Con loss, Str loss, and occasionally hallucinations.
• Sickness will eventually go away on its own if it’s not bad. Maybe look to FIQHack zombification disease for specific mechanics for how this could work.

Bed, a \ which if you sit on it makes you fall asleep for d10 turns or you have fully recovered your health. While sleeping on the bed, you get the same effects as hungerless regeneration. Found in barracks and some special levels. Breakfast not provided.

Poison is either changed or extended so that it is a lasting status condition that gives you negative HP regeneration, or some other source of this property is added.